Active ray-curable compositions that are cured by active energy radiation such as ultraviolet radiation or an electron beam, has been conventionally put to practical use in various applications such as coating materials for plastics, paper, wood and inorganic materials; adhesives, printing ink, printed circuit boards, and electric insulation connection.
Examples of inkjet ink systems using these polymerizable compositions include an ultraviolet-curable inkjet ink that is cured by ultraviolet radiation. The inkjet method that uses this ultraviolet-curable ink has attracted public attention in recent years, from the viewpoints of quick drying properties, and the ability to perform recording on a recording medium which lacks ink absorbability.
However, an image forming method utilizing these ultraviolet-curable inkjet systems has a problem that coalescence of adjoining dots, which causes a problem at the time of high speed recording (for example, in the case of a line recording method, a recording material conveyance speed of 30 m/s or more; and in the case of a serial recording method, a printing speed of 50 m2/hr or more) cannot be suppressed, and the image quality is deteriorated.
Furthermore, a hot melt ink system that uses a compound that undergoes phase change, such as wax, in the ink in an amount of 20% or more, is also attracting public attention from the viewpoint of enabling recording on ordinary paper that has not been subjected to special treatments, or on a recording medium that lacks ink absorbability. However, there is a problem that the film surface after image formation is easily peeled off with fingernails or the like.
There are known radiation-curable inks using a gelling agent, which are intended to solve these problems (see PTL 1 and PTL 2).
On the other hand, as a method of discharging air bubbles incorporated into an inkjet recording head at the time of the initial introduction of ink or at the time of head cleaning, it is known to provide a bubble discharge mechanism independently of ink droplet ejection (see PTL 3). Furthermore, as a method of preventing omitted injection or crooked flight that occurs at the time of continuous injection, there has been disclosed a technology of operating an actuator to transform the ink chamber partition walls, in such a manner that a predetermined rest time is provided between an extension pulse that extends the volume of the ink chamber by a contraction pulse that contracts the volume of the ink chamber (see PTL 4).